The present invention is generally in the field of measurement techniques and relates to a method and system for measuring patterned structures such as semiconductor wafers, by utilizing scatterometry. The invention is particularly useful for controlling a photolithography process.
Scatterometry based measurement techniques rely on measurement and interpretation of the characteristics of light diffracted from a regular array of lines (grating or pattern). Scatterometry provides the ability to accurately reconstruct the line profile, allowing the measurement of line width or lateral dimensions of the pattern (the so-called critical dimension (CD) of a patterned structure), height, profile wall angle and additional profile information. The analysis of diffraction measurements is usually carried out using exact models, such as RCWT, allowing for accurate reconstruction of the whole profile.
Critical dimensions can also be measured by a scanning electron microscope known as CD-SEM. The CD-SEM measurement technique is based on measuring the scattering efficiency of a focused electron beam, which is scanned over the sample area. CD-SEM thus provides an accurate top view image allowing for extracting different lateral dimensions, such as line width (CD).
Although both of the above indicated techniques are capable of measuring CD, measurements carried out by these techniques are completely different, and therefore usually lead to different measurement results. The differences between these two techniques generally consist of the following:
CD-SEM provides an image, while scatterometry does not CD-SEM measures separate lines, while scatterometry measures line arrays (gratings), affecting both the type of information, i.e., an average over the lines, and the required measurement site. CD-SEM provides only the top view of a pattern i.e., lateral information (CD), while scatterometry provides also the pattern height and profile information Additionally, the size and price of a scatterometry based measurement system and a CD-SEM are quite different.
There is a need in the art to improve the quality of measurements in patterned structures, such as semiconductor wafers by providing a novel measurement method and system.
The main idea of the present invention consists of combining the benefits of scatterometry and CD-SEM measurements by integrating a scatterometry measurement tool with a CD-SEM tool. While each of these tools has its relatively strong and weak sides (as compared to the other tool), the combined operation of these tools yields better results, both in terms of accuracy and in terms of additional profile information, than those that can be provided by using either one of these tools. Such a combination involves more than just putting the tools one beside the other but rather sharing information between the two tools thereby improving each one""s measurements beyond its current capability. Thus, a real added value is formed by the combination.
The physical integration of the two tools in a common system provides additional benefits, such as saving costs (e.g., common wafer handling system), increased through, reduced down time of the system, etc.
The applicability of the combined CDSEM-Scatterometry system according to the invention is not limited to any specific application. Typical applications requiring line width and line profile information can be found mainly, but not only, in the semiconductor and flat panel display fabrication industry, including, for example, microlithography (CD, photoresist profile, etc.), and etch (STI poly-silicone etch, trenches, etc.). Additional applications that require the profiling of repeatable features, which are arranged in a two-dimensional army such as via-holes, can also be measured using scatterometry and can thus benefit from the combined measurement system.
In accordance with one aspect of the present invention, there is thus provided a method of measuring g parameters of a patterned structure, the method comprising the steps of:
(i) applying scatterometry measurements to the structure and generating measured data indicative of the structure parameters;
(ii) applying scanning electron microscopy (SEM) measurements to the structure and generating measured data indicative of lateral pattern dimensions of the structure;
(iii) analyzing the entire measured data to use measurement results of either one of the scatterometry and SEM measurements for optimizing the other measurement results.
It should be understood that the measurement results are representative of real values of parameters extracted from the respective measured data.
According to another aspect of the invention, there is provided a measurement system for measuring parameters of a patterned structure, the system comprising:
(a) a scatterometry measurement tool operable to apply measurement to the structure and generate measured data indicative of the structure parameters;
(b) a scanning electron microscope (SEM) measurement tool operable to apply SEM measurements to the structure and generate measured data indicative of lateral pattern dimensions of the structure;
(c) a control system for operating the measurement tools to apply respective measurements, and analyzing the measured data so as to use measurement results of either one of the scatterometry and SEM measurement tools for opimizing measurement results of the other tool.
It should be understood that the term xe2x80x9ctoolxe2x80x9d (scatterometry tool or CD-SEM tool) signifies a set of constructional elements operating together to irradiate a sample with respective incident radiation, detect a radiation response of the sample and generate measured data indicative thereof. More specifically, the scatterometry measurement tool typically comprises a spectrophotometer, while the CD-SEM tool comprises an electron beam column and a detector, for example for detecting secondary electrons.
Generally, the construction and operation of each of these tools may be of any known kind. With respect to a scatterometry measurement tool, it is preferably constructed and operated as that disclosed in co-pending U.S. patent application Ser. No. 09/610,889, assigned to the assignee of the present application.
Thus, in the measurement system of the present invention, the scatterometry measurement tool and the SEM measurement tool are linked to each other for sharing measured data indicative of pattern-related information. This data sharing can be achieved in several ways:
According to one embodiment of the present invention, the two measurement tools are associated with the same database and the same control unit, such that data interpretation and reporting of measurement results are carried out by one controlling module, which has full control and full information over the two measurement tools.
According to another embodiment of the invention, the two measurement tools are associated with the same database, such that all information measured by either tool is stored within the same database, however, each tool is controlled by a separate control unit.
According to yet another embodiment of the invention, the two measurement tools are associated with separate databases and control units, respectively. In this case, however, the measurement tools can xe2x80x9crequestxe2x80x9d information from one another through a communication channel for any specific need (specific wafer specific measurement site, type of sites, etc.).
Additionally, the two measurement tools may be integrated in the physical sense, such that handling a measured sample is commonly done and controlled through a unified control unit. Such physical integration can be achieved in several ways. For example, the scatterometry measurement tool is applicable to a sample external to the CD-SEM chamber. In other words, a measurement zone of the scatterometry tool is located externally to the measurement zone of the CD-SEM. Another option consists of locating the scatterometry tool eternal to the CD-SEM chamber and locating the sample to be measured by both tools within the CD-SEM chamber. In this case, the chamber is formed with an optical window enabling scatterometry measurements through the window. Yet another possibility is to locate the scatterometry measurement tool and a sample to be measured inside the CD-SEM chamber.